U.S. Pat. No. 4,917,978 issued to P. M. Ritt et al., entitled, METHOD OF ELECTROPHOTOGRAPHICALLY MANUFACTURING A LUMINESCENT SCREEN ASSEMBLY HAVING INCREASED ADHERENCE FOR A CRT, discloses contacting dry-powdered phosphor particles, which have been surface-treated with a suitable polymer, with a solvent, to render the phosphor materials and an underlying photoconductive layer tacky to improve the adherence therebetween. Vapor soaking is described as the method of contacting the polymer-treated phosphor particles. Vapor soaking is achieved by positioning a particle-coated faceplate below a solvent-filled container which emits solvent vapors, which are heavier than air and thus flow downwardly to soak and soften the polymer on the phosphor particles as well as the underlying photoconductive layer. The faceplate is positioned upwardly, i.e., with the concave, particle-coated surface directed towards the container so that gravitational force can be utilized to increase the adherence of the softened particles to the photoconductive layer. A drawback of vapor soaking is that between 4 and 24 hours are required for the vapor soaking step.
U.S. Pat. No. 5,028,501, issued to Ritt et al., on Jul. 2, 1991, describes a "dry" filming process which includes the steps of depositing an electrostatically-charged, dry-powdered polymeric filming resin onto previously deposited screen structure materials, and then fusing the resin to form a substantially continuous film layer. The fusing step can be accomplished by heating the dry-powdered resin or by exposing the resin to a solvent. Three solvent exposure processes are recited: fogging, vapor deposition (soaking), and direct spray. Vapor soaking is described in the above-referenced patent application Ser. No. 299,507. While vapor soaking is the slowest of the three solvent exposure methods, it is the gentlest and least likely to disturb the polymer particles on the screen. A direct spray method is the fastest, but it tends to displace the polymer particles. The preferred vapor exposure process is atomizing or fogging, which combines the speed of the spray with the gentleness of the vapor soak. A need thus exists for an apparatus and method to perform fusing of polymer powders by fogging or atomizing a solvent.